Blade attachments are known from the prior art. They are often used to retrofit blades, which are already manufactured.
The blade attachment might be designed as an extension unit, which is used to prolong the length of the blade. The blade attachment might be designed as a winglet, which is used to change the aerodynamic characteristics of the wind turbine blade.
Blade attachments are used to adapt wind turbine blades to site-specific requirements for example.
Blade attachments are even used to prolong standardized blades if needed thus the efforts and complexities in blade-manufacturing tools and costs are reduced.
According to the prior art known the blade attachment overlaps a specified section of the wind turbine blade. The specified section is used for a glue-connection between the blade and its attachment thus a sufficient structural integration and connection of the two parts is reached.
FIG. 2 shows a blade attachment BA as known from the prior art.
The blade attachment BA is designed and prepared to prolong a blade (not shown here) in its length thus it is shaped and used as an extension unit of the blade.
The blade attachment BA comprises a core CO, which is made of foam or which is made of Balsa-wood for example.
The core CO is surrounded by a shell of a lamination LA, which preferably comprises a fiber reinforced lamination LA.
The lamination LA may comprise glass-fibers or glass-fiber-reinforced structures.
The core CO and the lamination LA are preferably connected by a matrix material like resin. The resin is preferably applied to the core-lamination-structure by help of a “vacuum assisted resin transfer moulding, VARTM”-process or VARTM abbreviated.
FIG. 3 shows a blade attachment BA as described in FIG. 2, which is connected to the tip end TE of a blade BL by help of glue.
The glue applied defines a glue-interface GI, which is between the tip end TE of the blade BL and the blade attachment BA.
The glue-interface GI is circumferential in view to the tip end TE of the blade BL and in view to the blade attachment BA. Thus the glue-interface GI is used as an environmental seal. Due to the environmental seal water infusion WI in the blade attachment BA is avoided or reduced at least.
Due to expected and long life cycle of wind turbine blades, which is 20 years or more, the glue-interface GI might get weaker over time.
Thus water WA might infuse the blade attachment BA. Due to the centrifugal forces of the rotating wind turbine blade BL the water WA moves through the porous core material to the tip end TEBA of the blade attachment BA.
The water WA typically accumulates within the blade attachment BA at its tip end TEBA. The water WA typically gathers within the porous material of the core CO.
The water is “trapped” at this position as the laminate LA surrounds the core CO like a shell SH.
At cold wind turbine sites the water WA might be turned into ice, thus cracks might be introduced into the shell SH.
The blade BL of the wind turbine and even its blade attachment BA is exposed to lightning strikes, thus the water WA might be turned into steam, resulting in a destroyed tip end TEBA of the blade attachment.